Cyanine dyes useful as desensitizers in a fogged, direct positive type of silver halide emulsion are known. U.S. Pat. No. 3,431,111 discloses certain cyanine dyes which contain an imidazo[4,5-b]quinoxaline nucleus. U.S. Pat. No. 4,025,347 discloses certain cyanine dyes containing an indole or indolenine nucleus carrying in the phenyl ring thereof a substituent of the benzoyl or phenyl-sulfonyl type.